Providing power based on state of charge

ABSTRACT

A modular and scalable power source can be used to supplement an existing source of power. In one embodiment, a DC source can be used to maintain a power source of a host system in a specific state in order to cause a desired behavior.

CLAIM OF PRIORITY

This application claims priority to U.S. Provisional Application No.60/957,926, “DC Source,” filed on Aug. 24, 2007, incorporated herein byreference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is related to the following applications andincorporated by reference herein in their entirety:

U.S. patent application Ser. No. ______ [Attorney Docket No.VALT-01000US0], entitled “Power Source,” by Alexander Choi, et al.,filed the same day as the present application;

U.S. patent application Ser. No. ______ [Attorney Docket No.VALT-01002US0], entitled “Power Source With Temperature Sensing,” byAlexander Choi, et al., filed the same day as the present application.

BACKGROUND

1. Field

The technology disclosed herein relates to power sources.

2. Description of the Related Art

The sophistication and uses of electrical devices have increaseddramatically. People have come to rely upon electrical devices fortransportation, business, education, health care, or for other needs.With the reliance on electric devices comes a reliance on the source ofpower for those electrical devices. For example, hybrid automobiles nowuse and rely on batteries to power the motor systems in order toincrease fuel efficiency, cellular communication systems rely on aconstant source of power to maintain the networks so that people can usetheir cellular telephones, and operating rooms rely on electricity topower many of the life saving devices used to treat patients. Other usesalso exist.

The increased use of and reliance on power presents a need for bettersources of power to supplement and/or replace existing sources of power.

SUMMARY

The technology described herein provides an improved power source thatcan be used to supplement and/or replace existing sources of power. Insome embodiments, the power source disclosed herein can be implementedas a scalable and modular DC source. This DC source can be used tocharge a battery in a host system, provide power as a back-up system, orbe a primary source of power.

One embodiment includes a controller, a battery in communication withthe controller, and a switch receiving an input from the battery and acontrol input from the controller. The switch provides power from thebattery at its output based on the control input from the controller. Inone example implementation, the battery includes a set of batterymodules connected in series. Each battery module includes multiplebattery cells connected in parallel. Each battery module also includes amonitor circuit that monitors one or more parameters of the battery andsends the one or more parameters to the controller. The controller usesthe parameters to control the battery.

One embodiment includes an application module capable of communicatingwith a host system according to a protocol for the host system, abattery management system in communication with the application module,and a battery in communication with the battery management system. Thebattery includes an output for providing power to the host system inresponse to the battery management system.

The technology described herein provides an improved power source thatcan supplement and/or replace existing sources of power. One embodimentincludes a method for providing power. The method includes receivingstate of charge information from a host about a power source for thehost and automatically providing charge to the power source for the hostfrom an auxiliary power source only if the state of charge informationindicates that the power source for the host is not meeting a target forstate of charge.

Another embodiment includes repeatedly receiving state of chargeinformation from a host about a power source for the host andmaintaining the power source for the host at a range of state of chargeby selectively providing and not providing charge to the power sourcefrom an auxiliary power source.

One embodiment includes repeatedly receiving information from a host andcausing a host to continue performing certain behavior by selectivelycharging a power source for the host based on the received information.

One embodiment includes a controller, a battery and a switch. Thecontroller includes an interface to a host system to receive state ofcharge information from the host system about a power source for thehost system. This switch receives a power signal from the battery and acontrol input from the controller. This switch selectively provides anddoes not provide power from the battery to the power source for the hostsystem based on the control input from the controller. The controllerprovides the control input to the switch based on the state of chargeinformation it receives from the host system.

The technology described herein provides an improved power source thatcan supplement and/or replace existing sources of power. One embodimentincludes a voltage sensor connected to a battery unit to sense voltagefor the battery unit, an alternative signal path around the batteryunit, a temperature sensor positioned to sense a temperature associatedwith the alternative signal path, and a comparator circuit. The voltagesensor adjusts the alternative signal path when the voltage sensorsenses that the voltage of the battery unit is above a target level. Thecomparator circuit compares an output of the temperature sensor to areference and adjusts the alternative signal path based on thatcomparison.

One embodiment includes monitoring voltages of a set of connectedbattery units, providing one or more alternative signal paths aroundeach of the battery units that reaches one or more target voltagelevels, monitoring temperatures of the alternative signal paths, andadjusting alternative signal paths that have reached one or morethreshold temperatures.

One embodiment includes monitoring voltage of a battery unit while thebattery unit receives a charging signal, adjusting an alternative signalpath around the battery unit to cause more of the charging signal to usethe alternative path if the voltage of the battery unit reaches a targetlevel, monitoring a temperature for the alternative path, and adjustingthe alternative path to cause less of the charging signal to use thealternative path if the temperature reaches a threshold temperature.

One embodiment includes a set of connected battery units and a set ofbalancing circuits connected to the battery units. The balancingcircuits each comprise a voltage sensor connected to a respectivebattery unit, an alternative signal path in communication with aterminal of the respective battery unit and a terminal of a battery unitconnected to the respective battery unit, a temperature sensorpositioned to sense temperature data for the alternative signal path,and a circuit. The circuit is in communication with the voltage sensor,the temperature sensor and the alternative signal path. The circuitadjusts the signal path in response to the voltage sensor sensing atarget voltage and adjusts the alternative signal path in response tothe temperature sensor sensing a threshold temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a system for providing a DC source.

FIG. 2 is a block diagram of a controller.

FIG. 3 is a block diagram of a controller.

FIG. 4 is a block diagram of a battery management system.

FIG. 5 is a block diagram of an application module.

FIG. 6A is a flowchart describing one embodiment of a process forcharging a battery of a host system.

FIG. 6B is a flowchart describing one embodiment of a process forcharging a battery of a host system.

FIG. 6C is a flowchart describing one embodiment of a process formonitoring current of a host battery and using that information to alterhow the host battery is charged.

FIG. 7 is a flowchart describing one embodiment of a process forcontrolling an auxiliary battery.

FIG. 8 is a circuit diagram describing one embodiment of a battery.

FIG. 9 is a circuit diagram describing one embodiment of a batterymodule.

FIG. 10 is a circuit diagram describing one embodiment of a batterystring.

FIG. 11 is a perspective view of a one battery cell.

FIG. 12 is a top view of a battery string.

FIG. 13 is a side view of a battery string.

FIG. 14 is a side view of a battery module.

FIG. 15 depicts the top view of the top plates of a battery module.

FIG. 16 is a side cut-away view of a battery cell.

FIG. 17 is a schematic diagram of one embodiment of a balancing circuit.

FIG. 18 is a flowchart describing one embodiment of a process of using acharge balancing circuit while charging a battery.

FIG. 19 depicts a circuit board for a charge balancing circuit.

FIG. 20 depicts a side view of the circuit board of FIG. 19.

FIG. 21 is a side cut-away view of FIG. 20.

FIG. 22 depicts a side view of battery module and a battery monitor.

FIG. 23 depicts a configuration for communication among multiple batterymonitors.

FIG. 24A is a flowchart describing one embodiment of a process for usingtemperature and voltage to control the system of FIG. 1.

FIG. 24B is a flowchart describing one embodiment of a process forpreventing deep discharge of the auxiliary battery.

FIG. 25 is a side view of the battery module.

FIG. 26 depicts twenty battery modules connected together.

FIG. 27 is a perspective view of a battery.

FIG. 28 is a perspective view of a battery.

FIG. 29 depicts a chassis for holding a battery.

FIG. 30 depicts an arrangement of battery modules that provides faulttolerance.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a system for providing a modular andscalable DC source. FIG. 1 depicts a controller 10 in communication withan auxiliary battery 12 and host 20. The system of FIG. 1 can providethe DC source in various different configurations. For example, in oneconfiguration, auxiliary battery 12 is used to charge a battery for host20. In another configuration, auxiliary battery 12 provides a back-uppower source for host 20. In another configuration, auxiliary battery 12can be used to provide a primary power source for host 20. Otherconfigurations can also be implemented.

Host 20 can be any device or system that uses a power source. In oneembodiment, host 20 is an automobile, such as a hybrid car. In anotherembodiment, host 20 can be a portion of a telecommunications network,equipment in an operating room, equipment in an emergency room, alighting system, or other system that uses electrical power. Thetechnology described herein is not limited to any particular host or anyparticular configuration for providing power to that host.

In one embodiment, host 20 includes host battery pack 22, host controlsystem 24, and host battery 26. Host battery pack 22 is a rechargeablebattery for host 20. In one embodiment, auxiliary battery 12 is used tocharge host battery pack 22. Host battery 26 is a battery. Host controlsystem 24 is a computer system or other electrical system. In oneembodiment, host control system 24 is in communication with host batterypack 22. In one example, host 20 is a hybrid automobile, host controlsystem 24 is a control system for a hybrid engine system, host batterypack 22 is a battery used to power the hybrid engine system when theengine system is in electric mode, and host battery 26 is a standardautomobile battery. One example of a hybrid automobile is the ToyotaPrius. As described above, the technology described herein is notlimited to an automobile.

In one example implementation, host 20 is not aware of controller 10,auxiliary battery 12, or other components of FIG. 1 that are not part ofhost 20. In other words, host 20 is not configured to receive powerspecifically from auxiliary battery 12.

FIG. 1 shows two sets of communication lines between controller 10 andhost control system 24. One of the lines is labeled EV mode only, whichis a signal asserted by controller 10 to host control system 24. In theembodiment where host 20 is a hybrid automobile, the signal EV mode onlycauses the automobile to operate in electricity only mode (e.g. withoutuse of gasoline). In some hybrid automobiles, this mode can be used whenthe automobile is operating at less than 34 miles per hour and the hostbattery pack 22 is at or greater than a predetermined minimum state ofcharge.

The second set of control lines between controller 10 and host 24 islabeled CAN Bus. Controller Area Network (CAN) is a broadcast,differential serial bus standard, originally developed for connectingelectronic control units (ECUs). CAN was specifically designed to berobust in electromagnetically noisy environments (such as in anautomobile) and can utilize a differential balanced line like RS-485. Itcan be even more robust against noise if twisted pair wire is used. Themessages sent on a CAN Bus are small (8 data bytes max) but areprotected by a CRC-15 (polynomial 0x62CC) that guarantees a Hamming bitlength of 6 (so up to 5 bits in a row corrupted will be detected by anynode on the bus). Bit rates up to 1 Mbit/s are possible at networklengths below 40 m. Decreasing the bit rate allows longer networkdistances (e.g. 125 kbit/s at 500 m). The CAN data link layer protocolis standardized in ISO 11898-1 (2003). This standard describes mainlythe data link layer—composed of the Logical Link Control (LLC) sublayerand the Media Access Control (MAC) sublayer—and some aspects of thephysical layer of the OSI Reference Model. All the other protocol layersare typically left to the network designer's choice.

In one embodiment, host control system 24, which is part of theautomobile sold by an automotive dealer, has a CAN Bus interface forimplementing one or more predefined protocols for communication withhost control system 24. Entities external to the automobile cancommunicate with host control system 24 using these one or moreprotocols. Examples of messages provided by host control 24 on the CANBus in one embodiment of the automobile with a hybrid engine includessuch state information as engine temperature, host battery pack 22current, host battery pack 22 voltage, host battery pack 22 state ofcharge, drive mode (P, R, N, D, B), vehicle speed, throttle, airbagdeployed, and EV mode (normal, EV mode, deny EV mode, cancel EV mode).

FIG. 1 also shows host battery 26 providing a DC voltage to controller10. In one embodiment, controller 10 uses the DC voltage from hostbattery 26 for power. Controller 10 is in communication with auxiliarybattery 12 using an RS-485 link. Controller 10 also sends a five volt DCsignal to auxiliary battery 12 in order to power electronics included inauxiliary battery 12. In one embodiment, controller 10 includes a DCconversion circuit which receives the voltage from host battery 26 andsteps it down to five volts for auxiliary battery 12.

Auxiliary battery 12 is a rechargeable battery that can be charged bycharger 30. An AC signal (AC) is provided to relay board 32. In oneembodiment, an electrical cord with a plug is connected to relay board32 and plugged into a standard electrical outlet. The relay boards ofFIG. 1 include electrically controlled mechanical switches that make theconnection between an input and output in response to a control signal.Other types of switches can also be used. Controller 10 sends one ormore control signals to relay board 32 indicating whether the relayboard should open or close its one or more switches. Relay board 32which is one example of a switch that can be used to turn on or off theAC input to charger 30 and cooling fan 34. Other switches can also beused. When controller 10 instructs relay board 32 to close the switches,the AC signal is provided at the output of relay board 32. The output ACsignal is provided to charger 30 and cooling fan 34. Therefore,controller 10 can turn on or off charger 30 and cooling fan 34. Whencharger 30 is turned on, cooling fan 34 is also turned on in order tocool auxiliary battery 12 while it is being charged. The output ofcharger 30 is connected to auxiliary battery 12 in order to chargeauxiliary battery 12.

FIG. 1 also shows a second cooling fan 36 connected to controller 10.The controller 10 sends a five volt DC signal to cooling fan 36 in orderto power cooling fan 36. In one embodiment, the five volt signal isprovided by a circuit which steps down the voltage from host battery 26.Controller 10 includes logic for turning on or off the power to coolingfan 36. Cooling fan 34 and cooling fan 36 are both positioned to be inproximity to auxiliary battery 12 so that they will cool battery 12. Inone embodiment, auxiliary battery 12 is housed in a box (see FIGS. 27and 28) that also includes both cooling fans.

The output of auxiliary battery 12 is provided to relay board 38.Controller 10 provides a control signal to relay board 38 whichindicates to relay board 38 whether to open or close its mechanicalswitches. When controller 10 instructs relay board 38 to close itsswitches, the power signal from auxiliary battery 12 is provided to theoutput of relay board 38. The output of relay board 38 is connected tocurrent sensing circuit 40.

Current sensing circuit 40 determines the current being drawn fromauxiliary battery 12 and reports that information to controller 10.Controller 10 can determine the current state of charge of auxiliarybattery 12 based on the current being drawn. There are many ways knownin the art for determining state of charge. One example scheme fordetermining state of charge is disclosed in U.S. patent application Ser.No. 11/394,726, filed on Mar. 31, 2006, titled “Battery ChargeIndication Methods, Battery Charge Monitoring Devices, RechargeableBatteries and Articles of Manufacture.” In one embodiment, currentsensing circuit 40 can be inside the same box as auxiliary battery 12.Some alternative embodiments include current sensing circuit 40 having afan for cooling current sensing circuit 40 and/or battery 12.

The power signal from auxiliary battery 12 that is provided to currentsensing circuit 40 is subsequently passed to relay board 42 from currentsensing circuit 40. The output of relay board 42 is provided to hostbattery pack 22. By controlling relay boards 38 and 42, controller 10determines when auxiliary battery 12 is providing power to host batterypack 22. In one implementation, controller 10 turns on or off theswitches in the relay boards in order to allow auxiliary battery 12 tocharge host battery pack 22. In the example where host battery pack 22is part of an automobile, such as a hybrid automobile, auxiliary battery12 can maintain host battery pack 22 at a certain state of charge orcharge host battery pack 22 when it is below a certain charge level.

Buzzer 50 and user interface 52 are in communication with controller 10.In one embodiment, controller 10 causes buzzer 50 to make a noise if afailure condition occurs (e.g. temperature of auxiliary battery is toohigh or state of charge of auxiliary battery is too low). Buzzer 50 canmake a sound for other conditions. User interface 52 includes a set oflight emitting diodes (LEDs). In one embodiment, there is one LED toindicate whether the system is running or not running, one LED toindicate whether the system is in EV only mode, and three or more LEDsto indicate the state of charge of auxiliary battery 12. In addition,user interface 52 can include a button that a driver of the automobile(or other type of user) can use to turn off the DC source of FIG. 1.

FIG. 2 is a block diagram describing one embodiment of controller 10.FIG. 2 shows processor 102 in communication with RS-485 interface 104,power control circuit 106, I/O interface 108, and CAN interface 110.Processor 102 can be any processor known in the art suitable for theparticular implementation. No specific processor is required. RS-485interface 104 provides a communication interface for communicating withauxiliary battery 12. Power control circuit 106 receives power from hostbattery 26 (see FIG. 1) and can step down the voltage to various othervoltages for powering processor 102, the other components of FIG. 2, andthe various components of FIG. 1. Additionally, processor 102 cancontrol power control circuit 106 to turn on, turn off, or otherwiseregulate the power provided to other components of FIG. 1 (e.g.auxiliary battery 12, cooling fan 36, and the other components of FIG.1). I/O interface 108 is an electrical circuit that provides aninterface to relay board 32, relay board 38, current sensing circuit 40,relay board 42, host control system 24 (EV mode only signal), buzzer 50,and user interface 52. In one embodiment, processor 102 can cause thesignal “EV mode only” to be asserted when the vehicle is driving lessthan 34 miles an hour and there is sufficient charge in auxiliarybattery 12. CAN interface 110 is an electrical circuit interface to theCAN Bus of host control system 24. CAN interface 124 provides thenecessary logic for communicating via the CAN bus. In an alternativeembodiment, controller 10 will be split into two modules: batterymanagement system 130 and application module 140. Battery managementsystem 130 controls communicates with battery 12 via the RS-485 link,controls the fans, and includes the I/O interface described above.Battery management system module 130 communicates with applicationmodule 140 via a CAN bus, which is a different CAN bus than that used tocommunicate with host control system 24. Application module 140 providesthe EV mode only signal and receives messages via the CAN bus from hostcontrol system 24. Application module 140 receives power from the hostand provides various power signals to different components of FIG. 1, asdescribed above. In the embodiment of FIG. 3, battery management system130 manages the auxiliary battery and is application independent, whileapplication module 140 is designed to interact with a specific host 20.Thus, if the system of FIG. 1 were to be used for different hosts, eachsystem would have the same battery management system 130 but differentapplication modules 140.

FIG. 4 is a block diagram depicting one example of battery managementsystem module 130. Processor 130 is in communication with RS-485interface 136, I/O interface 138, and CAN interface 134. RS-485interface 136 communicates with auxiliary battery 12 via the RS-485link. I/O interface 138 performs the same function as described abovewith respect to I/O interface 108. CAN interface 134 provides theinterface for processor 132 to communicate with application module 140via a CAN bus.

FIG. 5 is a block diagram describing one embodiment of applicationmodule 140. Processor 142 is communication with power control circuit144, CAN interface 146, and CAN interface 148. Power control circuit 144performs the same function as power control circuit 106. CAN interface146 provides an interface to a CAN bus between battery management system130 and application module 140. CAN interface 146 provides an interfacefor the CAN bus used to communicate with host control system 24.Processor 142 also provides the EV mode only signal. In someembodiments, there can be an I/O interface connected to processor 142for communicating the EV mode only signal.

FIG. 6 is a flowchart describing one embodiment of a process performedby controller 10 for controlling how auxiliary battery 12 is used tocharge host battery pack 22. Controller 10 receives messages from hostcontrol system 24 via the CAN bus depicted in FIG. 1. In oneimplementation, host control system 24 periodically sends messagesindicating the state of charge of host battery pack 22 (how charged hostbattery pack 22 is). FIG. 6 describes how controller 10 will use thatstate of charge information to apply and not apply charge from auxiliarybattery 12. In step 150 of FIG. 6, controller 10 receives a state ofcharge message from host control system 24. In step 152, it isdetermined whether the state of charge of host battery pack is greaterthan or equal to a threshold. If the state of charge of host batterypack 22 is greater than or equal to the threshold, then auxiliarybattery 156 is disconnected from host battery pack 22. For example,controller 10 can send a control message to relay board 42 and/or relayboard 38 to open the switches so that host battery pack 22 cannot drawany current from auxiliary battery 12. If, in step 152, it is determinedthat the state of charge of host battery pack 22 is not greater than orequal to the threshold, then in step 154 controller 10 will instructrelay board 42 and/or relay board 38 to close the switches and allowhost battery pack 22 to draw current from auxiliary battery 12. Theprocess of FIG. 6B can be performed every time a state of charge messageis received from the host. In some embodiments, state of charge messagesare received periodically. In other embodiments, FIG. 6 can be initiatedperiodically by controller 10 and can include a step where thecontroller 10 requests state of charge information from the host.

In one embodiment, the threshold used in step 152 is 75.5 percent. Forexample, in the implementation where host 20 is a hybrid automobile, thesystem of FIG. 1 is used to maintain host battery pack 22 at a targetlevel of approximately a 75.5 percent charge. In some hybridautomobiles, it has been observed that if the host battery pack is at75.5 percent charge, the vehicle will operate more often in electriconly mode. That is, the automobile will often think that its battery tobe highly charged and will attempt to use more battery than gas. Thiswill significantly increase gas mileage. Thus, the system of FIG. 1 willattempt to charge host battery pack 22 when it falls below 75.5 percentcharge by connecting the auxiliary battery 12 to the host battery pack.When the charge of the host battery pack gets to 75.5 percent ofcapacity or above, the auxiliary battery 12 will be disconnected fromthe host battery pack. Thus, by selectively charging the host batterypack 22 to a predetermined target level, the system of FIG. 1 can causethe host to continue performing a certain behavior (not using gas orlimiting the use of gas). In other embodiments that use other hosts,selectively charging a power source for that host can also be used tocause that host to continue to perform other behavior. The systemdescribed herein is not limited to any specific type of host orapplication. In one alternative, thresholds other than 75.5 percent canbe used, depending on the particular implementation.

In another embodiment, instead of maintaining the host battery pack 22at a predetermined state of charge (e.g., 75.5%), controller 10 canmaintain the host battery pack 22 at a predetermined range of state ofcharge. FIG. 6B is a flow chart that described a process for controller10 to maintain the host battery pack 22 at a predetermined range ofstate of charge. In step 158, controller 10 receives one or moremessages on the CAN bus from host control system 24 indicating the stateof charge of the host battery pack 22. In step 160, controller 10receives one or more messages on the CAN bus from host control system 24indicating the speed that host 20 is traveling (in the embodiment thathost 20 is a vehicle). In step 162, controller 20 uses the speedinformation to look-up an appropriate range of state of charge. Forexample, a table (or other data structure) can be stored that associatesdifferent speed values with a set of ranges of state of charge (SOC) ofhost battery pack 22. The table below provides one example.

Speed (mph) SOC range (start %) SOC range (stop %) 25 70 70.5 26 70 70.527 70 70.5 28 70.5 71 29 70.5 71 30 71 71.5 31 71 71.5 32 71 71.5 3371.5 72 34 71.5 72 35 72 72.5 36 72 72.5 37 72 72.5 38 72.5 73 39 72.573 40 73 73.5 41 73 73.5 42 73 73.5 43 73.5 74 44 73.5 74 45 74 74.5 4674 74.5 47 75 75.5 48 75.5 76 49 76 76.5 50 76.5 77Note that as the speed increases, the range also moves higher. Otherranges can also be used. In some embodiments, one or more of the rangescould be smaller than those listed above. For example, a range of one ormore state of charge values can be used.

In step 164, it is determined whether the state of charge of hostbattery pack 22 (as indicated in the message received in step 158) iswithin the appropriate range from the table of ranges. If so, thenauxiliary battery 156 is disconnected from host battery pack 22. Forexample, controller 10 can send a control message to relay board 42and/or relay board 38 to open the switches so that host battery pack 22cannot draw any current from auxiliary battery 12. If the state ofcharge of host battery pack 22 is outside and below the range identifiedin step 162, then in step 166 controller 10 will instruct relay board 42and/or relay board 38 to close the switches and allow host battery pack22 to draw current from auxiliary battery 12. The process of FIG. 6B canbe performed every time a state of charge message is received from thehost. In some embodiments, state of charge messages are receivedperiodically. In other embodiments, FIG. 6C can be initiatedperiodically by controller 10 and can include a step where thecontroller 10 requests state of charge information from the host.

In one embodiment, controller 10 will automatically disconnect auxiliarybattery 12 from host battery pack 22 if a message is received from hostcontrol system 24 on the CAN bus (see FIG. 1) that an airbag (or othersafety device) has deployed.

In one embodiment, controller 10 monitors the current of the hostbattery (from messages on the CAN bus) to prevent overcharging the hostbattery pack 22 from auxiliary battery 12 when host 20 is also charginghost battery pack 22. For example, a hybrid automobile may charge itsbattery during braking through regenerative braking and it may bedesirable not to provide too much charge from auxiliary battery 12during that time. FIG. 6C is a flowchart describing one embodiment of aprocess for adjusting how auxiliary battery is used to charge hostbattery pack 22. In step 170, controller 10 receives a message on theCAN bus indicating the current of host battery pack 22 (host batterypack 22 current). If that current is non-negative (step 172), then noaction is taken with respect to changing how auxiliary battery is usedto charge host battery pack 22. If that current is negative (step 172),then it is determined (in step 176) whether auxiliary battery 12 hasbeen connected to charge host battery pack 22 for two or more seconds.If auxiliary battery 12 has been connected to charge host battery pack22 for two or more seconds, then auxiliary battery 12 is disconnectedfrom host battery pack 22 (e.g., stop charging) in step 178 and thesystem will wait for one second (step 180), during which auxiliarybattery 12 will remain disconnected from host battery pack 22. Afterstep 180, the system will resume performing the process of FIG. 6A, FIG.6B, or another suitable process used to connect/disconnect auxiliarybattery 12 from host battery pack 22. Note that a negative currentindicates that host battery pack 22 is being charged by host 20. Ifauxiliary battery 12 has been connected to charge host battery pack 22for less than two seconds, then it is determined whether the messagereceived in the most recent iteration of step 170 was the first orsecond consecutive message indicating a negative current.

If the message received in step 170 was the first message indicating anegative current, then in step 184 the auxiliary battery 12 isdisconnected from host battery pack 22 (e.g., stop charging). In step186, controller 12 stores an indication that it has received the firstmessage indicating a negative current (for which the auxiliary batterywas connected for less than 2 sec.). Other time values can also be used.In step 188, the system will wait for two seconds, during whichauxiliary battery 12 will remain disconnected from host battery pack 22.Other time values can also be used. After step 188, the system willresume performing the process of FIG. 6A, FIG. 6B, or another suitableprocess used to connect/disconnect auxiliary battery 12 from hostbattery pack 22.

If the message received in step 170 was the second consecutive messageindicating a negative current (two consecutive iterations of step 170indicated negative current), then in step 190 the auxiliary battery 12is disconnected from host battery pack 22 (e.g., stop charging). In step192, controller 12 stores an indication that it has received the secondconsecutive message indicating a negative current (for which theauxiliary battery was connected for less than 2 sec.). Other time valuescan also be used. In step 194, the system will wait for five seconds,during which auxiliary battery 12 will remain disconnected from hostbattery pack 22. Other time values can also be used. After step 194, thesystem will resume performing the process of FIG. 6A, FIG. 6B, oranother suitable process used to connect/disconnect auxiliary battery 12from host battery pack 22.

If the message received in step 170 was the third or more consecutivemessage indicating a negative current (two consecutive iterations ofstep 170 indicated negative current), then in step 196 the auxiliarybattery 12 is disconnected from host battery pack 22 (e.g., stopcharging). In step 198, the system will wait for ten seconds, duringwhich auxiliary battery 12 will remain disconnected from host batterypack 22. Other time values can also be used. After step 198, the systemwill resume performing the process of FIG. 6A, FIG. 6B, or anothersuitable process used to connect/disconnect auxiliary battery 12 fromhost battery pack 22. Note that when step 174 is performed because thehost battery pack is being discharged rather than charged, controllerwill reset to zero its indication of consecutive message indicating anegative current.

The process of FIG. 6C can be performed every time a host battery packcurrent message is received from the host. In some embodiments, hostbattery pack current messages are received periodically. In otherembodiments, FIG. 6C can be initiated periodically by controller 10 andcan include a step where the controller 10 requests current informationfrom the host.

As described above, current sensing circuit 40 provides information tocontroller 10 about the current being drawn from auxiliary battery 12 byhost 20. FIG. 7 is a flowchart describing one embodiment of howcontroller 10 uses that information from current sensing circuit 40. Instep 160 of FIG. 7, controller 10 receives an indication of the currentbeing drawn from auxiliary battery 12. This information is received fromcurrent sensing circuit 40. In step 162, controller 10 uses the dataabout current drawn from auxiliary battery 12 in order to determine thestate of charge of auxiliary battery 12. In step 164, it is determinedwhether the state of charge of the auxiliary battery 12 is greater thana threshold. If the state of charge of the battery is greater than thatthreshold, then ordinary operation will continue at step 168. Forexample, the system will continue to operate according to FIG. 6.However, if in step 164 it is determined that the state of charge of thebattery is below the threshold, then auxiliary battery 12 will bedisconnected from host 20. For example, step 166 can include controller10 causing relay boards 38 and 42 to open the switches and preventcurrent from being drawn from auxiliary battery 12 regardless of whetherthe process of FIG. 6 is attempting to connect or disconnect theauxiliary battery. One embodiment of a threshold for use in step 164 issixty percent. Other thresholds can also be used. In one embodiment, thestate of charge used in steps 160-168 is based on the entire auxiliarybattery 12. In other embodiments, the decision in step 164 can be basedon whether any individual module within battery 12 or any individualstring (see discussion below) within battery 12 is below a particularstate of charge. The exact number to be used for the threshold in step164 is based on the design of the particular auxiliary battery and canbe varied based on different implementations of auxiliary battery 12.

FIG. 8 is a schematic diagram of one embodiment of auxiliary battery 12.In one example implementation, auxiliary battery 12 includes 20 batterymodules connected in series with each other. For example, FIG. 8 showsbattery module 1, battery module 2, battery module 3, battery module 4,battery module 5, battery module 6, battery module 7, battery module 8,battery module 9, battery module 10, battery module 11, battery module12, battery module 13, battery module 14, battery module 15, batterymodule 16, battery module 17, battery module 18, battery module 19 andbattery module 20 connected in series with each other. In otherimplementations, more or less than twenty battery modules can be used.In one embodiment, each battery module includes four battery stringsconnected in series with each other. For example, FIG. 9 shows a batterymodule with four battery strings connected in series. In otherembodiments more or less than four strings (e.g., two or more strings)can be included in a battery module. FIG. 10 shows a schematic of anexample battery string that includes twenty four battery cells connectedin parallel with each other. Note that other arrangements of batterymodules, battery strings and battery cells can also be used. The examplearrangement of battery modules/strings/cells connected in parallel andin series are made to allow the auxiliary battery to be both modular andscalable. For example, the batteries connected in series increasevoltage based on each battery connected in series. Batteries connectedin parallel increase capacity of the energy storage.

FIG. 11 depicts a perspective view of one battery cell 200. In oneembodiment, battery cell 200 is a 1.4 amp hour cell with 3.2 voltsnominal voltage. FIG. 12 shows a top view of twenty four battery cells200 that are part of a battery string. The view of FIG. 12 shows thebattery cells 200 but does not show the connections of the batterycells. The connections have been removed to depict the top of thebattery cells. FIG. 13 is a side view of the same battery string thatincludes 24 battery cells 200. However, for clarity sake, not all of thecells have been labeled. The side view of FIG. 13 shows plate 210 andplate 212 which connect the battery cells 200 in parallel. More detailsof the connections will be provided with respect to FIGS. 14 and 15.

FIG. 14 shows a side view of a battery module with four battery strings.One battery cell from each string can be seen from the view of FIG. 14.For example, battery cell 200 a is from a first battery string, batterycell 200 b is from a second battery string, battery cell 200 c is from athird battery string and battery cell 200 d is a from a fourth batterystring. The first battery string that includes battery cell 200 a hasall the battery cells connected in parallel by welding their negativeterminals to plate 210 and welding their positive terminals to plate212. In one embodiment, plates 210 and 212 are nickel plates that arewelded to copper plates. The battery string that includes battery cell200 b has the positive terminals of the battery cells in the stringwelded to plate 214 and the negative terminals welded to plate 216.Plates 214 and 216 are nickel plates welded to copper plates. Thebattery string that includes battery cell 200 c has the negativeterminals of all the battery cells in the string welded to plate 220 andthe positive terminals of all the battery cells connected in that stringare welded to plate 202. In one embodiment, plates 220 and 202 arenickel plates welded to copper plates. The battery string that includesbattery cell 200 d has the positive terminals of all the battery cellsin the string welded to plate 224 and the negative terminals are allwelded to plate 202. In one embodiment, plates 202 and 224 are nickelplates welded to copper plates. Rivet 230 is welded to both plates 212and 220 to connect the two strings in series. Rivet 232 is welded toboth plates 216 and 224 to connect the two strings in series. Plate 202connects to two strings. Plate 210 provides a negative terminal for thebattery module. Plate 214 provides a positive terminal for the batterymodule. Because each of the battery cells in the string are connectedvia rigid plates and the various strings are connected together by rigidrivets (e.g. rivets 230 and 232) and rigid plate 212, without the use ofwires, the battery module is better able to withstand vibration.

FIG. 15 depicts the top view of plate 210 and plate 214. As can be seenthe left edge of plate 210 includes a set of holes and the right edge ofplate 214 includes a set of holes. Plate 214 is in the shape of arectangle. Plate 210 is generally in the shape of a rectangle; however,one edge has a profile resembling a series of rounded edges. The variousmodules are connected together by aligning plate 210 of one module withplate 214 of another module so that the holes of plate 210 align withthe holes of plate 214. Screws can be inserted through some or all ofthe holes to hold the modules together. These modules are, therefore,connected using a ridged connection, without the use of wires, in orderto better withstand vibration. By using rigid connections instead ofwires, the batteries will not come apart due to vibration from drivingor other sources of vibration.

FIG. 16 depicts one example of battery cell 200. Other types of batterycells can also be used. FIG. 16 depicts a cylindrical secondaryelectrochemical battery cell 200. In one embodiment, battery cell 200includes a spirally coiled or wound electrode assembly 312 enclosed in asealed container, preferably a rigid cylindrical casing 314. In analternate embodiment, the architecture of the secondary electrochemicalcell is that of a z-fold design, wound prismatic or flat-plate prismaticdesign, or polymer laminate design.

The electrode assembly 312 includes: a positive electrode 316, a counternegative electrode 318 and a separator 320 interposed between thepositive and negative electrodes 316, 318.

The separator 320 is preferably an electrically insulating, ionicallyconductive microporous film, and composed of a polymeric materialselected from the group consisting of polyethylene, polyethylene oxide,polyacrylonitrile and polyvinylidene fluoride, polymethyl methacrylate,polysiloxane, copolymers thereof, and admixtures thereof.

Each electrode 316, 318 include a current collector 322 and 324,respectively, for providing electrical communication between theelectrodes 316, 318 and an external load. Each current collector 322,324 may be a foil or grid of an electrically conductive metal such asiron, copper, aluminum, titanium, nickel, stainless steel, or the like,having a thickness of between 5 μm and 100 μm, preferably 5 μm and 20μm. Optionally, the current collector may be treated with anoxide-removing agent such as a mild acid and the like, and coated withan electrically conductive coating for inhibiting the formation ofelectrically insulating oxides on the surface of the current collector322, 324. Examples of suitable coatings include polymeric materialscomprising a homogenously dispersed electrically conductive material(e.g. carbon), such polymeric materials including: acrylics includingacrylic acid and methacrylic acids and esters, including poly(ethylene-co-acrylic acid); vinylic materials including poly(vinylacetate) and poly(vinylidene fluoride-co-hexafluoropropylene);polyesters including poly(adipic acid-co-ethylene glycol);polyurethanes; fluoroelastomers described herein below; and mixturesthereof.

The positive electrode 316 further includes a positive electrode film326 formed on at least one side of the positive electrode currentcollector 322, preferably both sides of the positive electrode currentcollector 322, each film 326 having a thickness of between 10 μm and 150μm, preferably between 25 μm an 125 μm, in order to realize the optimalcapacity for the cell 200. The positive electrode film 326 is preferablycomposed of between 80% and 99% by weight of a positive electrode activematerial described herein below as general formula (I), between 1% and10% by weight binder, and between 1% and 10% by weight electricallyconductive agent.

The negative electrode 318 is formed of a negative electrode film 328formed on at least one side of the negative electrode current collector324, preferably both sides of the negative electrode current collector324. The negative electrode film 328 is composed of between 80% and 95%of an intercalation material, between 2% and 10% by weight binder, and(optionally) between 1% and 10% by of an weight electrically conductiveagent.

Suitable electrically conductive agents include: natural graphite (e.g.flaky graphite, and the like); manufactured graphite; carbon blacks suchas acetylene black, Ketzen black, channel black, furnace black, lampblack, thermal black, and the like; conductive fibers such as carbonfibers and metallic fibers; metal powders such as carbon fluoride,copper, nickel, and the like; and organic conductive materials such aspolyphenylene derivatives.

Binders suitable for use in the positive electrode 316 include:polyacrylic acid; carboxymethylcellulose; diacetylcellulose;hydroxypropylcellulose; polyethylene; polypropylene;ethylene-propylene-diene copolymer; polytetrafluoroethylene;polyvinylidene fluoride; styrene-butadiene rubber;tetrafluoroethylene-hexafluoropropylene copolymer; polyvinyl alcohol;polyvinyl chloride; polyvinyl pyrrolidone;tetrafluoroethylene-perfluoroalkylvinyl ether copolymer; vinylidenefluoride-hexafluoropropylene copolymer; vinylidenefluoride-chlorotrifluoroethylene copolymer; ethylenetetrafluoroethylenecopolymer; polychlorotrifluoroethylene; vinylidenefluoride-pentafluoropropylene copolymer; propylene-tetrafluoroethylenecopolymer; ethylene-chlorotrifluoroethylene copolymer; vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer; vinylidenefluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer;ethylene-acrylic acid copolymer; ethylene-methacrylic acid copolymer;ethylene-methyl acrylate copolymer; ethylene-methyl methacrylatecopolymer; styrene-butadiene rubber; fluorinated rubber; polybutadiene;and admixtures thereof. Of these materials, most preferred arepolyvinylidene fluoride and polytetrafluoroethylene.

Intercalation materials suitable herein include: transition metaloxides, metal chalcogenides, carbons (e.g. graphite), and mixturesthereof capable of intercalating the alkali metal-ions present in theelectrolyte in the electrochemical cell's nascent state.

In one embodiment, the intercalation material is selected from the groupconsisting of crystalline graphite and amorphous graphite, and mixturesthereof, each such graphite having one or more of the followingproperties: a lattice interplane (002) d-value (d(002)) obtained byX-ray diffraction of between 3.35 Å to 3.34 Å, inclusive (3.35Å≦d(002)≦3.34 Å), preferably 3.354 Å to 3.370 Å, inclusive (3.354Å≦d(002)≦3.370 Å; a crystallite size (Lc) in the c-axis directionobtained by X-ray diffraction of at least 200 Å, inclusive (Lc≧200 Å),preferably between 200 Å and 1,000 Å, inclusive (200 Å≦Lc≦1,000 Å); anaverage particle diameter (Pd) of between 1 μm to 30 μm, inclusive (1μm≦Pd≦30 μm); a specific surface (SA) area of between 0.5 m2/g to 50m2/g, inclusive (0.5 m2/g≦SA≦50 m2/g); and a true density (ρ) of between1.9 g/cm³ to 2.25 g/cm³, inclusive (1.9 g/cm³≦ρ≦2.25 g/cm³).

Referring again to FIG. 16, to ensure that the electrodes 316, 318 donot come into electrical contact with one another, in the event theelectrodes 316, 318 become offset during the winding operation duringmanufacture, separator 320 “overhangs” or extends a width “a” beyondeach edge of the negative electrode 318—in one embodiment 50 μm≦a≦2,000μm. To ensure alkali metal does not plate on the edges of the negativeelectrode 318 during charging, the negative electrode 318 “overhangs” orextends a width “b” beyond each edge of the positive electrode 316. Inone embodiment, 50 μm≦b≦2,000 μm.

The cylindrical casing 314 includes a cylindrical body member 330 havinga closed end 332 in electrical communication with the negative electrode318 via a negative electrode lead 334, and an open end defined bycrimped edge 336. In operation, the cylindrical body member 330, andmore particularly the closed end 332, is electrically conductive andprovides electrical communication between the negative electrode 318 andan external load (not illustrated). An insulating member 338 isinterposed between the spirally coiled or wound electrode assembly 312and the closed end 332.

A positive terminal subassembly 340 in electrical communication with thepositive electrode 316 via a positive electrode lead 342 provideselectrical communication between the positive electrode 316 and theexternal load (not illustrated). Preferably, the positive terminalsubassembly 340 is adapted to sever electrical communication between thepositive electrode 316 and an external load/charging device in the eventof an overcharge condition (e.g. by way of positive temperaturecoefficient (PTC) element), elevated temperature and/or in the event ofexcess gas generation within the cylindrical casing 314. Suitablepositive terminal assemblies 340 are disclosed in U.S. Pat. No.6,632,572 to Iwaizono, et al., issued Oct. 14, 2003; and U.S. Pat. No.6,667,132 to Okochi, et al., issued Dec. 23, 2003. A gasket member 344sealingly engages the upper portion of the cylindrical body member 330to the positive terminal subassembly 430.

A non-aqueous electrolyte (not shown) is provided for transferring ioniccharge carriers between the positive electrode 316 and the negativeelectrode 318 during charge and discharge of the electrochemical cell200. The electrolyte includes a non-aqueous solvent and an alkali metalsalt dissolved therein (most preferably, a lithium salt).

Suitable solvents include: a cyclic carbonate such as ethylenecarbonate, propylene carbonate, butylene carbonate or vinylenecarbonate; a non-cyclic carbonate such as dimethyl carbonate, diethylcarbonate, ethyl methyl carbonate or dipropyl carbonate; an aliphaticcarboxylic acid ester such as methyl formate, methyl acetate, methylpropionate or ethyl propionate; a .gamma.-lactone such asγ-butyrolactone; a non-cyclic ether such as 1,2-dimethoxyethane,1,2-diethoxyethane or ethoxymethoxyethane; a cyclic ether such astetrahydrofuran or 2-methyltetrahydrofuran; an organic aprotic solventsuch as dimethylsulfoxide, 1,3-dioxolane, formamide, acetamide,dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane,ethyl monoglyme, phospheric acid triester, trimethoxymethane, adioxolane derivative, sulfolane, methylsulfolane,1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone a propylenecarbonate derivative, a tetrahydrofuran derivative, ethyl ether,1,3-propanesultone, anisole, dimethylsulfoxide and N-methylpyrrolidone;and mixtures thereof. A mixture of a cyclic carbonate and a non-cycliccarbonate or a mixture of a cyclic carbonate, a non-cyclic carbonate andan aliphatic carboxylic acid ester, are preferred.

Suitable alkali metal salts, particularly lithium salts, include:LiClO4; LiBF4; LiPF6; LiAlCl4; LiSbF6; LiSCN; LiCF3SO3; LiCF3CO2;Li(CF3SO2)2; LiAsF6; LiN(CF3SO2)2; LiBlOCl10; a lithium lower aliphaticcarboxylate; LiCl; LiBr; LiI; a chloroboran of lithium; lithiumtetraphenylborate; lithium imides; and mixtures thereof. Preferably, theelectrolyte contains at least LiPF6.

As noted herein above, the positive electrode film 326 contains apositive electrode active material represented by the general formula(1):

AaMbLcZd,  (I)

wherein:

(i) A is selected from the group consisting of elements from Group I ofthe Periodic Table, and mixtures thereof, and 0≦a≦9;

(ii) M includes at least one redox active element, and 0≦b≦4;

(iii) L is selected from the group consisting of X[O4-x,Y′x],X′[O4-y,Y′2y], X″S4, [Xz′″,X′1-z]O4, and mixtures thereof, wherein:

-   -   (a) X′ and X′″ are each independently selected from the group        consisting of P, As, Sb, Si, Ge, V, S, and mixtures thereof,    -   (b) X″ is selected from the group consisting of P, As, Sb, Si,        Ge, V, and mixtures thereof,    -   (c) Y′ is selected from the group consisting of halogens        selected from Group 17 of the Periodic Table, S, N, and mixtures        thereof, and    -   (d) 0≦x≦3, 0≦y≦2, 0≦z≦1 and 0≦z≦3; and

(iv) Z is selected from the group consisting of a hydroxyl (OH), ahalogen selected from Group 17 of the Periodic Table, and mixturesthereof, and 0≦e≦4; and

wherein A, M, L, Z, a, b, c and d are selected so as to maintainelectroneutrality of the positive electrode active material in itsnascent or “as-synthesized” state.

As used herein, the term “redox active element” includes those elementscharacterized as being capable of undergoing oxidation/reduction toanother oxidation state when the electrochemical cell is operating undernormal operating conditions. As used herein, the term “normal operatingconditions” refers to the intended voltage at which the cell is charged,which, in turn, depends on the materials used to construct the cell.

Methods of making the electrode active materials described by generalformula (I), as well as electrochemical cells containing the same, aredescribed in: WO 01/54212 to Barker et al., published Jul. 26, 2001;International Publication No. WO 98/12761 to Barker et al., publishedMar. 26, 1998; WO 00/01024 to Barker et al., published Jan. 6, 2000; WO00/31812 to Barker et al., published Jun. 2, 2000; WO 00/57505 to Barkeret al., published Sep. 28, 2000; WO 02/44084 to Barker et al., publishedJun. 6, 2002; WO 03/085757 to Saidi et al., published Oct. 16, 2003; WO03/085771 to Saidi et al., published Oct. 16, 2003; WO 03/088383 toSaidi et al., published Oct. 23, 2003; U.S. Pat. No. 6,203,946 to Barkeret al., published Mar. 20, 2001; U.S. Pat. No. 6,387,568 to Barker etal., issued May 14, 2002; U.S. Pat. No. 6,528,033 to Barker et al.,issued Mar. 4, 2003; U.S. Pat. No. 7,008,566 to Barker et al., publishedMar. 7, 2006; U.S. Pat. No. 7,026,072 to Barker et al., published Apr.11, 2006; U.S. Publication No. 2003/0027049 to Barker et al., publishedFeb. 2, 2003; U.S. Publication No. 2002/0192553 to Barker et al.,published Dec. 19, 2002; U.S. Publication No. 2003/0170542 to Barker atal., published Sep. 11, 2003; and U.S. Publication No. 2003/1029492 toBarker et al., published Jul. 10, 2003; U.S. Publication No.2004/0131939 to Adamson et al., published Jul. 8, 2004; U.S. PublicationNo. 2003/0190526 to Saidi et al., published Oct. 9, 2003; U.S.Publication No. 2003/0190527 to Saidi et al., published Oct. 9, 2003;U.S. Publication No. 2003/0190528 to Saidi et al., published Oct. 9,2003; U.S. Ser. No. 11/746,142 filed May 9, 2007 entitled “SecondaryElectrochemical Cell With Increased Current Collecting Efficiency”; theteachings of all of which are incorporated herein by reference.

Non-limiting examples of electrode active materials represented bygeneral formula (I) include the following:

LiFePO4; LiCoPO4, LiMnPO4; LiMn0.8Fe0.2PO4; LiMn0.9Fe0.8PO4;LiFe0.9Mg0.1PO4; LiFe0.8Mg0.2PO4; LiFe0.95Mg0.05PO4;LiFe0.95Nb_(0.05)PO4; Li1.025Cu0.85Fe0.05Al0.025Mg0.05PO4,Li1.025Cu0.80Fe0.10Al0.025Mg0.05PO4,Li1.025Cu0.75Fe0.15Al0.025Mg0.05PO4,Li1.025Cu0.7(Fe0.4Mn0.6)0.2Al0.025Mg0.05PO4,LiCo0.8Fe0.08Al0.025Ca0.05PO3.975F0.025,LiCo0.8Fe0.1Al0.025Mg0.05PO3.975F0.025,

LiCo0.8Fe0.1 Ti0.025Mg0.05PO4;

Li1.025Cu0.8Fe0.1 Ti0.025Al0.025PO4; Li1.025Cu0.8Fe0.1Ti0.025Mg0.025PO3.975F0.025; LiCo0.825Fe0.1 Ti0.025Mg0.025PO4;LiCu0.85Fe0.075Ti0.025Mg0.025PO4; LiVOPO4; Li(VO)0.75Mn0.25PO4;Li3V2(PO4)3; Li3Fe2(PO4)3; Li3Mn2(PO4)3; Li3FeTi(PO4)3; Li3CoMn(PO4)3;Li3FeV(PO4)3; Li3VTi(PO4)3; Li3FeCr(PO4)3; Li3FeMo(PO4)3; Li3FeNi(PO4)3;Li3FeMn(PO4)3; Li3FeAl(PO4)3; Li3FeCo(PO4)3; Li3Ti2(PO4)3;Li3TiCr(PO4)3; Li3TiMn(PO4)3; Li3TiMo(PO4)3; Li3TiCo(PO4)3;Li3TiAl(PO4)3; LiVPO4F; Li0.6VPO4F0.6; Li0.8VPO4F0.8; LiVPO4F;Li3V2(PO4)2F3; LiVPO4Cl; LiVPO4OH; NaVPO4F; Na3V2(PO4)2F3;LiV0.9Al0.1PO4F; LiFePO4F; LiTiPO4F; and LiCrPO4F.

Although examples of battery cells are provided above, other batterycells can also be used with the technology described herein.

Each battery string includes a charge balancer. The charge balancer isused during the charging of auxiliary battery 12. If one of the batterystrings becomes fully charged, it may stop conducting current. Thecharge balancer can bypass a fully charged battery string. In oneembodiment, the charge balancer will completely bypass a fully chargedbattery. In another embodiment, charge balancer will provide analternative current path around the battery string to the next batterystring in the series connection of battery strings. In one embodiment,the alternative path functions similar to resistor so that current willnot be completely bypassing the battery. Rather, a large percentage ofthe current will use the alternative path, with some current stilldirected at the fully charged battery string. In one embodiment, abattery cell is completely charged at 3.65 volts. A charge balancercircuit can be used to provide the alternative path around a batterystring when any one battery cell reaches 3.65 volts. In alternativeembodiments, there can be separate charge balancers for each batterycell so that when any one battery cell reaches 3.65 volts (or anotherthreshold), then only that one fully charged battery cell will bebypassed rather than the entire battery string. Each charge balancer canbe implemented as a circuit on a board, in an integrated circuit, or inanother means. No specific mode of implementation is required.

FIG. 17 is a schematic diagram of one embodiment with a charge balancercircuit that can be used with a battery string. BJT transistor 402 hasits emitter connected to the positive terminal of the battery string andits collector connected to resistor 404. The other side of resistor 404is connected to LED 406, which is used to indicate operation of thecharge balancing circuit. The base of transistor 402 is connected toresistor 408. The other side of resistor 408 is connected to resistor410, which is connected to the base of BJT transistor 414. The emitterof transistor 414 is connected to the base of BJT transistor 416 and thecollector of transistor 414 is connected to the collector of transistor416. The collector of transistor 416 is connected to the negativeterminal of the battery string and the positive terminal of the nextbattery string in series. The emitter of transistor 416 is connectedback to the positive terminal of the battery string. Transistors 414 and416 are in a Darlington configuration in order to operate as a variableresistor. Capacitor 420 is connected between resistors 408 and 410. Theother side of capacitor 420 is connected to the collector of transistor422. The positive terminal of the battery string is connected toresistors 424 and 430. The other side of resistor 424 is connected todiode 426 and capacitor 420. Resistor 430 is also connected to resistor428. Diode 426, resistor 428 and the emitter of transistor 422 are allconnected to the negative terminal of the battery string and thepositive terminal of the next battery string in series. The base oftransistor 422 is connected to resistor 432 which is also connected toresistors 438, resistor 434 and the output of comparator 450. Resistor438 is also connected to the negative terminal of the battery string andthe positive terminal of the next battery string in series. Resistor 434is connected to LED 436.

Comparator 450 includes two inputs. The first input includes thepositive terminal of the battery string across resistor 452. The secondinput to comparator 450 is connected to the output of comparator 456.The output of comparator 456 is also connected to resistor 454 and diode462. Resistor 454 is also connected to the negative terminal of thebattery string and the positive terminal of the next battery string inseries.

Comparator 456 has two inputs. One input is connected to resistors 458,460 and 464. Resistor 460 is also connected to diode 462. Resistor 458is also connected to the negative terminal of the battery string and thepositive terminal of the next battery string in series. The other end ofresistor 464 is connected between diode 468 and resistor 470. Resistor470 is also connected to the positive terminal of the battery string.Diode 468 is also connected to the negative terminal of the batterystring and the positive terminal of the next battery string in series.The second input to comparator 456 is connected to the output oftemperature sensor 474 and capacitor 472.

Temperature sensor 474 is a LM60 temperature sensor from NationalSemiconductor Corporation. Temperature sensor 474 receives power (AMP)from charge pump 482. One example of a suitable charge pump is a LM2662from National Semiconductor Corporation. The charge pump provides a 5volt output signal. The power signal received by temperature sensor 474is also connected to capacitor 476. The output of charge pump 482 isprovided to temperature sensor 474 via capacitor 488. Charge pump 482receives its power from the positive terminal of the battery string,which is also connected to capacitor 490. Capacitor 484 is the chargepump capacitor and is connected to the CAP+ and CAP− pins of the chargepump.

Sample values for the resistors in the circuit of FIG. 17 are asfollows:

Resistor 404 680 ohms Resistor 408 100k ohms Resistor 410 10 ohmsResistor 424 680 ohms Resistor 428 10k ohms Resistor 430 4.7k ohmsResistor 432 10k ohms Resistor 434 680 ohms Resistor 438 10k ohmsResistor 452 1k ohms Resistor 454 10k ohms Resistor 460 100k ohmsResistor 458 68k ohms Resistor 464 100k ohms Resistor 470 200 ohms

Example capacitates used are as follows:

Capacitor 420 0.1 uF Capacitor 476 0.1 uF Capacitor 472 0.1 uF Capacitor44 10 uF

In operation, when the voltage across a battery string is 3.65 volts,based on the voltage divider comprising resistor 428 and resistor 430,then the shunt regulator turns on which draws a current from the base oftransistor 414. Drawing current from the base of transistor 414 causes acurrent to flow across transistor 416. The emitter of transistor 416 isconnected to the positive terminal of the battery string. The collectorof transistor 416 is connected to the negative terminal of the batterystring and positive terminal of the next battery string in series.Therefore, transistor 416 provides the alternative path around thebattery string.

Temperature sensor 474 is constantly sensing the temperature. The outputof temperature sensor 474 is a voltage indicative of temperature beingsensed. Comparator 456 compares the output of the temperature sensor toa reference voltage. If the temperature is too high, then the output ofcomparator 456 causes the shunt regulator to turn off, closing off thealternative path provided by transistor 416. This temperature safetyfeature is provided because transistor 416, when used as an alternativepath for current, can become very hot. To help dissipate heat,transistors 414 and 416 are mounted to a heat sink. Temperature sensor474 is also mounted to the heat sink or is mounted in close proximity tothe heat sink in order to measure temperature of the heat sink. Thetemperature of the heat sink is indicative of the temperature of thealternative path. When transistor 416 and, therefore, the heat sink,gets too hot, the alternative path provided by transistor 416 is turnedoff. When it cools down, it can be turned on again.

FIG. 18 is a flowchart describing one embodiment of a process foroperation of a charge balancer. In step 502, a charge will be applied toauxiliary battery 12. For example, the AC input to relay board 32 can beplugged into an AC outlet, therefore, providing alternate current forcharging the battery. That alternate current is provided to charger 30which provides a charge signal to auxiliary battery 12. In step 504,auxiliary battery 12 is charged by charger 30.

While auxiliary battery 12 is being charged, steps 506-512 are performedby each charge balancer for its associated battery string. In oneembodiment, steps 506-512 are performed continuously. In otherembodiments, steps 506-512 are performed periodically, depending on thedesign of the charge balancer. In step 506, the charge balancer monitorsvoltage of the battery string. In step 508, the charge balancer monitors(or measures) the temperature of the alternate path. For example, thetemperature sensor can monitor the temperature of the heat sink ordirectly monitor the temperature of transistor 416, either of which isindicative of the temperature of the alternate path. In one embodiment,steps 506 and 508 are performed continuously and simultaneously.

In step 510, it is determined whether the associated battery string (orany battery cell) is fully charged. In one embodiment, a battery stringis determined to be fully charged if the voltage across the string is3.65 volts. Additionally, the process of determining whether to bypass abattery string can be made for voltages that are lower than a fullycharged voltage. If the battery string is not fully charged, then thealternative path is not used (step 512). Not using the alternative pathcould include completely turning off the alternate path or configuringthe alternative path to only conduct a small or nominal amount ofcurrent.

If the battery string (or battery cell) is fully charged (step 510),then it is determined whether the temperature of the alternative path(e.g., temperature of the heat sink or other temperature indicative ofthe temperature of the alternative path) is less than a thresholdtemperature. In some embodiments, the threshold temperature is 105° C.Other values for the temperature threshold can also be used, dependingon the particular design implemented. If the temperature is not greaterthan the threshold temperature, then that battery string that has beendetermined to be fully charged is provided with an alternative currentpath (step 516). If the temperature is greater or equal to the thresholdtemperature, then the alternate path is not used.

Providing the alternative path can include adjusting the alternativepath to turn on the alternative path or increasing the current conductedby the alternative path from a nominal level to a level that effectivelyreduces the charge provided to the string. When stopping the use of thealternative path in step 518, the alternative path can be adjusted tostop all flow of current or reduce the flow of current to a nominallevel.

In one embodiment, each battery module will include its own set of fourcharge balancer circuits. Each module will include two circuit boardsconnected together in a T configuration. These two circuit boards,combined, will include the four charge balancer circuits for thatmodule. FIGS. 19, 20, and 21 depict the two circuit boards 520 and 530for implementing the charge balancer. The first circuit board 520 isdivided into four sections 521, 522, 523 and 524. Section 521 is for afirst charge balancer circuit for a first battery string of the batterymodule. Section 522 of circuit board 520 is for the components of acharge balancer for a second battery string of the battery module.Section 523 is for the components of a charge balancer for a thirdbattery string of the battery module. Section 524 is for the componentsof a charge balancer for a fourth battery string of the battery module.The second circuit board 530 is connected to circuit board 520 in a Tconfiguration. FIG. 19 is a top view showing the two circuit boards 520and 530 with circuit board 530 coming out of the page (e.g. Zdirection). FIG. 20 provides a side view of circuit boards 520 and 530looking in the direction of arrow 519 (see FIG. 19).

Circuit board 530 also includes four sections, one for each chargebalancer circuit of the battery module. For each charge balancercircuit, one side of circuit board 530 includes a heat sink and theother side of circuit board 530 includes transistors 414 and 416(represented by box 418) and temperature circuit 480 (which includestemperature sensor 474). As can be seen from FIG. 20, the components arealternated with having the heat sink on one side for the first and thirdcharge balancer circuits and the heat sink is on the other side for thesecond and fourth charge balancer circuits. As can be seen from FIG. 21,the heat sink is connected to the transistors 418 by vias filled in withcopper. Heat is transferred from the transistors to the heat sink 550 bythe vias. Temperature sensor circuit 480 is similarly connected to heatsink 550 by vias. In alternate embodiments, temperature sensor 474 canbe connected to heat sink 550 by mounting it on the same side as heatsink 550 on circuit board 530. Note that FIG. 21 is a side view ofboards 520 and 530 by cutting away the boards along dash line 552 andlooking in the direction of arrow 554.

In one embodiment, the charge balancer can be implemented in anintegrated circuit. The embodiment discussed above contemplates onecharge monitor per string. However, if the charge balancer isimplemented in an integrated circuit, or if space is not an issue, thecan be one charge balancer per battery cell.

Each battery module also includes a battery monitor circuit whichincludes two temperature sensors connected in parallel for each batterystring and one voltage sensor for each battery string. The batterymonitor circuit monitors the temperature and voltage for each batterystring and communicates that data to controller 10. FIG. 22 is a blockdiagram of the side view of the battery module and the battery monitorelectronics. FIG. 22 shows voltage sensors 602 and temperature sensors604. There are two temperature sensors 604 connected to each string. Inone embodiment, the temperature sensor is four thermisters on a flexiblecircuit. The flexible circuits are mounted to the side of each string sothat each battery cell in the string is in contact with the flexiblecircuit. The temperature sensors send their data to Analog-to-Digital(A/D) converter 610 which provides digital versions of all the datasensed to processor 612. Voltage sensors 602 and connected to eachbattery string. Each of the voltage sensors provide a digital voltagevalue to processor 612. Processor 612 will also receive temperature andvoltage data from another processor 612 of an adjacent battery mode.Processor 612 will package the data from its battery module with thedata from other battery modules received from the adjacent batterymodule at the input CM_IN and provide the package data to its outputCM_OUT.

In one embodiment, there will be a battery monitor for each batterymodule. Therefore, in the embodiment with twenty battery modules, therewill be twenty battery monitors. For example, FIG. 23 shows twentybattery monitors. There are many ways for the battery monitors tocommunicate their data to controller 10. In one embodiment, each batterymonitor will individually communicate its data to controller 10. Inanother embodiment, the battery monitors will be connected in a daisychain fashion. Each battery monitor will provide its data to a batterymonitor of an adjacent battery module. For example, FIG. 23 shows eachof the battery monitors connected in a daisy chain fashion. Batterymonitor 1 CM1 provides its data (voltage and temperature data) to itsneighboring battery monitors, CM2, via its output CM1_OUT. CM2 willreceive the data from CM1, package it with its own temperature andvoltage data, and send the packaged data out on its output line CM2_OUTto the next battery monitor, CM3. Battery monitor CM3 will package itsvoltage and temperature data with the data received from CM2 (whichincludes data from the CM1 and CM2), and provide that packaged data toCM4. This process will continue until the point that CM19 provides thedata for CM1-CM19 to CM20. CM20 will package its data with the data fromall the other battery monitors and provide the data to an RS-485interface for communication to controller 10 via the RS 485 linkdiscussed above with respect to FIG. 1. In some embodiments, controller10 can also provide information and commands back to all the batterymonitors via the same or different RS-485 link.

In one alternative, the battery monitor can be implemented in anintegrated circuit. In some alternatives, there will be one integratedcircuit for each battery cell. This will allow the controller 10 to turnon or off any battery cell based on data for the individual batterycell.

FIG. 24A is a flowchart describing one embodiment of the operation ofcontroller 10 with respect to the data received from the batterymonitors. In step 600, controller 10 receives and stores voltage datafrom the battery monitors. In step 602, controller 10 receives andstores the temperature data from the battery monitors. In oneembodiment, step 600 and step 602 are performed by receiving the datapackaged as a group from battery monitor 20 (FIG. 23). Step 600 and step602 are performed continuously and repeatedly. While performing steps600 and 602, controller 10 will also perform step 620-636. In step 620,controller 10 determines whether any module is hotter than a toptemperature. In one embodiment, the top temperature is 65° C. If anymodule is hotter than the top temperature, then controller 10 will turnoff the entire system of FIG. 1 (except for the host) in step 622. Inone embodiment, controller 10 may also sound buzzer 50 to alert theuser. If no modules are above the top temperature (step 620), thencontroller 10 determines whether any module is hotter than a triggertemperature. In one embodiment, the trigger temperature is 35° C. If anyone module is greater than the trigger temperature, then controller 10will turn on cooling fan 36 in step 626. If no module is greater thanthe trigger temperature (step 624), then controller 10 will determinewhether any module is greater than the trigger voltage. In oneembodiment, the trigger voltage is 3.6 volts. If any module is greaterthan the trigger voltage than controller 10 will turn on cooling fan 36.If no module is greater than the trigger voltage (step 628), thencontroller 10 will determine whether any module is less than the resettemperature. If a module is less than the reset temperature, thencooling fan 36 will be turned off in step 634. Otherwise, there will beno change (step 636). Steps 620-636 can be performed periodically.

FIG. 24B is a flow chart describing one embodiment of how controller 10uses the voltage data from the battery monitors to prevent auxiliarybattery 12 from being discharged too deeply. As indicated in FIG. 24A,controller 10 repeatedly receives voltage data for all of the batterystrings. As described with respect to FIG. 23, the voltage data for allbattery strings is packaged together and provided to controller 10 fromCM20. Each time the set of voltage data is provided to controller 10 isreferred to as a cycle. In other embodiments, voltage data for a batterystring (or other unit of battery elements) is provided for a cycle in adifferent manner than as described with respect to FIG. 23, such asdirectly from each battery monitor. After data for a cycle is providedto controller 10, the process of FIG. 24B is performed.

In step 650 if FIG. 24B, controller looks for any battery string whosevoltage data indicates that the battery string has a voltage less thanan alert level. In some embodiments, the process of FIG. 24B can beperformed for units other than a battery string. In step 652, controller10 determines whether any battery string had a voltage less than thealert level for X consecutive cycles. If not, then the process of FIG.24 is done (and will start again at the next cycle). If controller 10determines that any battery string had a voltage less than the alertlevel for X consecutive cycles, then in step 654 the system waits tenseconds, during which the auxiliary battery 12 remains disconnected (notcharging) host battery pack 22. Other time values can also be used. Instep 656, X more cycles of data are received. In step 658, controller 10determines whether any battery string (the same as the string in step652 or a different one) had a voltage less than the alert level for thelast X consecutive cycles. If not, then the process of FIG. 24 is done,will reset, and will start again at the next cycle (step 668). Ifcontroller 10 determines that any battery string had a voltage less thanthe alert level for the last X consecutive cycles, then in step 660,auxiliary battery 12 is disconnected (not charging) host battery pack 22and remains disconnected until it is charged again. In step 662,controller 10 will activate a warning to the user. For example, awarning LED on user interface 52 will be turned on. In step 664,auxiliary battery 12 is charged, the process of FIG. 24 will reset, andthe process will start again at the next cycle.

In one embodiment, the process of FIG. 24B is performed differentlybased on whether auxiliary battery 12 is connected to (charging) hostbattery pack 22. If auxiliary battery 12 is connected to (charging) hostbattery pack 22, then X is twenty four cycles and the alert level is 2.5volts. If auxiliary battery 12 is not connected to (not charging) hostbattery pack 22, then X is eighteen cycles and the alert level is 1.5volts. Other alert levels and other values of X can also be used. Insome examples, X could be as low as one. In one alternative, the systemcould trigger suspension (step 654) or shutdown (step 658) if M voltagevalues for a battery string during X cycles are below the alert level,where 0<M≦X.

FIG. 25 is a side view of a battery module 700. On one end of batterymodule 700 is circuit board 702 which includes the battery monitorcircuit. On the other end of battery module 700 are circuit boards 520and 530 which include the four charge balancer for battery module 700.Battery module 700 includes four strips of tape 710 which help to holdthe battery cells in place. Also depicted on the side of module 700 aretwo of the temperature sensors 604. Behind temperature sensor 604 andtape 710 can be seen the various battery cells 200 of two of the batterystrings. The other two strings are hidden behind.

FIG. 26 shows twenty battery modules connected together. FIG. 26 alsoshows the circuit board 702 for the charge balancers for each module anda wire connecting each of the charge balancers to an adjacent chargebalancer. The set of connected battery modules depicted in FIG. 26 arehoused in a box, for example, box 800 of FIG. 27. In one embodiment, box800 includes all of the components of FIG. 1 except for buzzer 50, userinterface 52, and host 20. Box 800 includes two apertures to accommodatethe cooling fans. For example one side of the box includes an aperturedefined by frame 806. FIG. 28 shows box 800 from a differentperspective. As can be seen in FIG. 28, the other side of box 800includes a second aperture 807. Box 800 will have a third aperture (orset of apertures) for connecting wires from box 800 to the host. Thisthird aperture is not depicted in the figures.

Box 800 is positioned in chassis 802. FIG. 29 shows chassis 802 withoutbox 800. Chassis 802 includes a circular opening 808 that aligns withaperture 807 of box 800. Chassis 802 is mounted to a surface for storingthe DC system of FIG. 1. A pair of arms 804 and 810 connect chassis 802to box 800. In one embodiment, arms 804 and 810 are hydraulic arms. Arm804 is connected to box 800 at connection point 820. Arm 810 isconnected to box 800 at connection point 822. Box 800 can be lifted fromchasse 802 by manually lifting box 800 which actuates the hydraulic armsand causes box 800 to lift and pivot.

In one embodiment, the system of FIG. 1 is used to charge a battery of ahybrid automobile. In that example, chasse 802 is mounted in the rearcargo space of the automobile. In one embodiment where the automobile isa Toyota Prius, chassis 802 is mounted above the spare tire. When box800 is positioned inside chassis 802, the top of box 800 is on the samelevel as the cargo area surface. By lifting and pivoting box 800 usingthe hydraulic arms, the contents of box 800 can be accessed and thespare tire can be accessed.

In one alternative, the battery modules of auxiliary battery 12 can bebroken up into groups of battery modules. FIG. 30 shows the batterymodules divided into five groups; however, more or less than five groupscan be used. Each group of battery modules includes four battery modulesconnected in series and connected to a DC to DC converter circuit. Forexample battery modules group one is connected to DC to DC convertercircuit 902, battery modules group two is connected to DC to DCconverter circuit 904, battery modules group three is connected to DC toDC converter circuit 906, battery modules group four is connected to DCto DC converter circuit 908, and battery modules group five is connectedto DC to DC converter circuit 910. The DC to DC converter circuitsreceive an input DC signal and provide an output DC signal at adifferent voltage. In one embodiment, the DC to DC converter circuitscreate a higher voltage than the input voltage based on input from thecontroller. The outputs from each of the DC to DC converter circuits arecombined and the combined power is provided to the host. Each of the DCto DC converter circuits 902-910 are in communication with controller10. If any one of the battery modules fails, controller 10 will detectthe failure and instruct the corresponding DC to DC converter circuit toturn off the voltage output. If a battery modules group fails, the DC toDC converter circuit will output a zero voltage for that battery modulesgroup. The remaining battery modules groups will have theircorresponding DC to DC voltages converter circuits adjusted in responseto controller 10 to provide higher voltages so that the combined signalis close to or the same as the voltage that would have been provided ifall of the battery module groups were functional. In this way, the hostreceives the same power regardless of whether all or a subset of batterymodules are functioning properly. In this matter, the arrangement ofFIG. 30 provides a more full tolerant battery system. In one embodiment,controller 10 can detect that a battery modules group has failed basedon the data from the battery monitor circuits or from an additionalmonitoring circuit.

The foregoing detailed description has been presented for purposes ofillustration and description. It is not intended to be exhaustive or tolimit to the precise form disclosed. Many modifications and variationsare possible in light of the above teaching. The described embodimentswere chosen in order to best explain the principles of the disclosedtechnology and its practical application, to thereby enable othersskilled in the art to best utilize the technology in various embodimentsand with various modifications as are suited to the particular usecontemplated. It is intended that the scope of be defined by the claimsappended hereto.

1. A method for providing power, comprising: receiving state of chargeinformation from a host about a power source for said host; andautomatically providing charge to said power source for said host froman auxiliary power source only if said state of charge informationindicates that said power source for said host is not meeting a targetfor state of charge.
 2. A method according to claim 1, wherein: saidtarget is a target voltage level; charge is provided to said powersource for said host from said auxiliary power source only if said stateof charge information indicates that said power source for said host hasa current state of charge below said target voltage level.
 3. A methodaccording to claim 1, wherein: said host is a hybrid automobile; saidpower source for said host is a rechargeable battery for a hybrid enginesystem for said hybrid automobile; said auxiliary power source is abattery that is selectively connected and disconnected to saidrechargeable battery; and said automatically providing charge to saidpower source for said host includes maintaining said rechargeablebattery for said hybrid engine system at high enough charge to avoidsaid hybrid engine system from using gas.
 4. A method according to claim1, wherein: said receiving state of charge information includesreceiving messages from said host over a communication bus.
 5. A methodaccording to claim 1, wherein: said automatically providing charge tosaid power source for said host from said auxiliary power source only ifsaid state of charge information indicates that said power source forsaid host is not meeting said target for state of charge includesopening and closing relays that connect said auxiliary power source tosaid power source for said host.
 6. A method according to claim 1,wherein said automatically providing charge to said power sourceincludes: receiving speed information for said host; using said speedinformation to determine a range, said target for state of charge issaid range; determining whether said state of charge informationindicates that said power source for said host has a state of chargewithin said range; and providing charge to said power source for saidhost if said state of charge information indicates that said powersource for said host has a state of charge is outside said range.
 7. Amethod according to claim 1, wherein: said automatically providingcharge to said power source for said host from said auxiliary powersource only if said state of charge information indicates that saidpower source for said host is not meeting said target for state ofcharge includes attempting to maintain said power source for said hostat a predetermined state of charge.
 8. A method according to claim 1,further comprising: determining a state of charge for said auxiliarypower source; and stopping use of said auxiliary power source if saiddetermined state of charge for said auxiliary power source is below atrigger.
 9. A method according to claim 1, further comprising:determining multiple state of charge values for said auxiliary powersource, said auxiliary power source comprises multiple battery unitsconnected together, said determining multiple state of charge valuesincludes determining state of charge values for each of said batteryunites; and stopping use of battery units having state of charge valuesbelow a trigger.
 10. A method according to claim 1, further comprising:monitoring temperature of said auxiliary power source; monitoringvoltage of said auxiliary power source; activating a cooling system ifsaid temperature is above a first level or said voltage is above a firstvoltage; and stopping use of said auxiliary power source if saidtemperature is above a second level.
 11. A method according to claim 1,further comprising: receiving a message from said host that a safetydevice has deployed; and stopping use of said auxiliary power source inresponse to said message.
 12. A method according to claim 1, furthercomprising: receiving a message from said host that an airbag hasdeployed, said host is an automobile; and stopping use of said auxiliarypower source in response to said message.
 13. A power source,comprising: a controller, said controller includes an interface to ahost system to receive state of charge information from said host systemabout a power source for said host system; a battery; and a switchreceiving an input from said battery and a control input from saidcontroller, said switch selectively provides and does not provide chargefrom said battery to said power source for said host system based onsaid control input from said controller, said controller provides saidcontrol input based on said state of charge information.
 14. A powersource according to claim 13, wherein: said controller instructs saidswitch, via said control input, to provide charge from said battery tosaid power source only if said power source is below a threshold stateof charge.
 15. A power source according to claim 14, wherein: saidcontroller instructs said switch, via said control input, to providecharge from said battery to said power source only if said power sourceis within a range of charge.
 16. A power source according to claim 13,wherein: said interface to a host system is an interface to anautomobile.
 17. A method for providing power, comprising: repeatedlyreceiving state of charge information from a host about a power sourcefor said host; and maintaining said power source for said host at arange of state of charge by selectively providing and not providingcharge to said power source for said host from an auxiliary powersource.
 18. A method according to claim 17, wherein: said receivingstate of charge information includes receiving messages from anautomobile about a hybrid engine system's battery; and said maintainingsaid power source for said host at said range of state of chargeincludes maintaining said battery at said range of state of charge toreduce said hybrid engine system's use of gasoline.
 19. A methodaccording to claim 17, further comprising: determining a state of chargefor said auxiliary power source; and stopping use of said auxiliarypower source if said determined state of charge for said auxiliary powersource is below a trigger.
 20. A method according to claim 17, furthercomprising: monitoring temperature of said auxiliary power source;increasing a cooling system if said temperature is reaches a firstlevel; and stopping use of said auxiliary power source if saidtemperature reaches a second level.
 21. A method according to claim 17,further comprising: monitoring voltage of said auxiliary power source;determining whether said voltage reaches a first voltage; and increasinga cooling system if said voltage is above said first voltage.
 22. Amethod for providing power, comprising: repeatedly receiving informationfrom a host; and causing a host to continue performing certain behaviorby selectively charging a power source for said host based on saidinformation.
 23. A method according to claim 22, wherein: said host isan automobile with a hybrid engine system; said power source for saidhost is a battery for said automobile; said certain behavior includesoperation with reduced use of gasoline; said causing includesselectively providing charge to said battery for said automobile from arechargeable auxiliary battery.
 24. A method according to claim 22,wherein: said information is about said power source for said host. 25.A method according to claim 22, wherein: said information includes stateof charge information regarding said power source for said host; andsaid selectively charging a power source for said host based on saidinformation includes maintaining said power source at a range of stateof charge.